Spatial dynamics of methane emissions and organic load reduction in a pond-based palm oil mill effluent treatment...

Palm oil mill effluent (POME) treatment in open pond systems is a significant source of methane (CH₄) emissions, yet the spatial dynamics of greenhouse gas fluxes and organic matter degradation remain poorly quantified. This study investigated CH₄, carbon dioxide (CO₂), and nitrous oxide (N₂O) emissions alongside chemical oxygen demand (COD) reductions across a full-scale, pond system consisting of 10 ponds connected in series (Pond 1 to 10) in Sarawak, Malaysia. Using a novel, low-cost, remotely operated floating chamber, we conducted high-resolution spatial sampling of gas fluxes and water quality. The results revealed extreme heterogeneity in COD removal and CH₄ fluxes, with a critical emission hotspot identified in Pond 4, where average CH₄ flux exceeded 900 μmol m^-2 s^-1 and COD decreased by over 80 %. Stoichiometric analysis confirmed a strong correlation between removed COD and CH₄ production. The cumulative climate impact of the system was estimated at 278 kg CO₂-equiv. m^-3 of treated effluent, with over 85 % of emissions attributed to CH₄. These findings highlight the need for targeted emission mitigation strategies, such as biogas capture from high-emission ponds, and provide robust emission factors to inform sustainable palm oil wastewater management and climate policy frameworks.